JP3105992B2 - Fuel storage device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel storage rack for storing a fuel body before or after use in a nuclear reactor, and a fuel storage device such as a fuel transport / storage container.

[0002]

2. Description of the Related Art A fuel assembly generally used in a boiling water reactor is provided with a handle 2 at an upper end thereof as shown in a perspective view of an upper part of FIG. It is surrounded by the channel box 3. The channel box 3 is integrally locked by a fastener 4.

[0003] In the channel box 3 below the handle 2, a number of fuel rods (not shown) are regularly arranged by an upper tie plate, a lower tie plate, and spacers to form a bundle. Handle 2 on the upper tie plate provided
Are attached to form the fuel assembly 1.

In the following description, the bundle formed by a large number of fuel rods, an upper tie plate, a lower tie plate and spacers is called a normal fuel bundle, and this fuel bundle is housed in a channel box 3. This is referred to as a fuel assembly 1. Further, the fuel bundle and the fuel assembly 1 are collectively referred to as a fuel assembly.

[0005] A fuel body before or used in a nuclear reactor is stored in a fuel storage rack installed in a fuel storage pool of a nuclear reactor facility for a certain period of time. And
If necessary, it is loaded into the reactor or stored in a fuel transport / storage container. The function required for the fuel storage device such as the fuel storage rack and the fuel transport / storage container is that a large number of fuel assemblies can be arranged as densely as possible while maintaining the subcritical state of the fuel body sufficiently.

A plan view of FIG. 9 and a perspective view of an upper part of FIG. 10 show a fuel storage rack 5 which is an example of a fuel storage device, and an outer shape of a fuel assembly 1 which is a fuel body is substantially a prism. Therefore, in order to arrange the fuel assemblies as densely as possible, a plurality of square-shaped fuel storage tubes 6 for storing the fuel assemblies are arranged in a square shape, and the periphery is surrounded by a large container 7. The fuel storage rack 5 in the initial stage has a structure in which a gap is provided between each fuel storage pipe 6 in order to maintain a sufficient subcritical state of a large number of stored fuel bodies, so that the fuel bodies are stored more densely. This was an obstacle to the above.

On the other hand, stainless steel, which is inexpensive and has sufficient strength, is mainly used as a structural material constituting the fuel storage rack 5, but this is an obstacle to storing many fuel bodies more densely. Recently, a fuel storage rack made of stainless steel to which a neutron absorbing material such as boron is added has been developed to eliminate the cause. Although the fuel storage rack 5 has been described above, the development history of other fuel storage devices is the same.

[0008]

There is a period of several years before the operation of a full-scale nuclear fuel reprocessing facility that accepts spent nuclear fuel is started. The performance required of storage facilities is becoming increasingly sophisticated. Even after the full-scale operation of the nuclear fuel reprocessing facility has started, the efficiency of transporting spent nuclear fuel from the nuclear power generation facility to the nuclear fuel reprocessing facility, and receiving and storing spent nuclear fuel at the nuclear fuel reprocessing facility, It is desirable that the fuel bodies be stored more densely. For this purpose, the technique of storing many fuel bodies more densely while maintaining a sufficient subcritical state has become an even more important issue.

[0009] However, in order to store a fuel body more densely while maintaining a sufficient subcritical state, as described above, as described above, a stainless steel to which a neutron absorbing material such as boron is added has been developed. And related mainly to the improvement of structural materials of the fuel storage device. However,
Generally, when a neutron absorbing material such as boron is added to a metal material such as stainless steel, the material tends to harden or become brittle, or to impair workability and soundness.

[0010] For example, it is considered difficult to use a stainless steel material containing a certain amount (2% by weight) of boron or more as a structural material. Therefore, in improving the performance of the fuel storage device, the technique of improving the structural material of the fuel storage device is considered to be close to its limit. In addition, when a newly developed metal material is used as a structural material for a fuel storage device, various tests such as checking its soundness are required, and there is a problem that a long period of time is required for practical use. Was.

It is an object of the present invention that the fuel body storage height position of an arbitrary fuel storage pipe is different from the fuel body storage height position of one or more adjacent fuel storage pipes. By using a structure that differs only by the length that can increase the criticality safety most effectively within the range without the above, dense storage and criticality safety are high while using metal materials such as stainless steel used conventionally. An object of the present invention is to provide a fuel storage device that can be put into practical use in a relatively short time.

[0012]

SUMMARY OF THE INVENTION In a fuel storage device comprising a plurality of fuel storage tubes for storing fuel bodies, the positions of any fuel storage pipes adjacent to each other in the axial direction of the fuel body storage are adjacent.
That the effective fuel length of the fuel body including the region where the reactivity is locally high in the fuel body axial direction of the fuel body or the plurality of fuel storage pipes in the fuel body axial direction is 3/24 to 5/24. Features.

[0013]

[Function] The fuel body storage height position of an arbitrary fuel storage pipe is 3/24 to 5/24 of the active fuel length of the fuel body in the fuel body storage height position of the adjacent fuel storage pipe and the fuel body height direction. By storing the fuel assemblies in the different fuel storage devices, there is no locally high-reactivity region near the upper and lower ends of each fuel assembly, and it is possible to improve dense storage and more critical safety. it can. Further, since this effect can be realized by using a metal material which has been used in the past, it is possible to confirm the function for practical use in a relatively short time.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings, taking a fuel storage rack for storing a spent fuel assembly of a boiling water reactor as an example. The same components as those of the above-described conventional technology are denoted by the same reference numerals, and detailed description thereof will be omitted.
As shown in the plan view of FIG. 1 and the bottom vertical sectional view taken along the line AA in FIG. 1 of FIG. 2, and the upper perspective view of FIG. A total of 16 fuel storage pipes (hereinafter abbreviated as L pipes) 12 having a low fuel storage height position (hereinafter abbreviated as H pipes) 11 are arranged in a square of 4 × 4,
The outer circumference is fixed by surrounding it with a large container 13 and the fuel storage rack 10
Is composed.

FIG. 1 shows a state in which the same fuel storage height position is arranged in the vertical direction and the fuel storage height positions different in the horizontal direction are alternately arranged. Further, at the bottom of the H pipe 11, the position of the storage height 14 is about 3/24 to 5/24 of the fuel effective portion of the fuel assembly 1 which is the fuel body to be stored. As an example of increasing the storage position, As shown in FIG. 2, a pedestal 15 is provided at the bottom of the H tube 11. The H tube 11 and the L tube 12 are manufactured by integrally forming four tubes each other and alternately arranging them. The H tube 11 and the L tube 12 are, as shown in FIG. Since the space is held by the wall of the large vessel 13 at the outer periphery, the H pipe 11 and the L pipe 12 do not always need to be individually provided, and the H pipe 11 and the L pipe 12 do not need to be integrally manufactured. .

Next, the operation of the above configuration will be described. Subcritical neutron flux (φ) when neutron source (intensity S) is given in infinite homogeneous system or single point system
It is well known that the following equation (1) is related to the effective neutron multiplication factor (k _eff : hereinafter abbreviated as k) via a proportional coefficient α. φ = αS / (1-k) (1)

The value of k has been considered to be constant irrespective of the location of the system in the conventional general knowledge of reactor physics. For example, a spent fuel assembly of a boiling water reactor is submerged in water. It is easy for a person involved in reactor physics to understand that when one body is placed, there is almost no probability that neutron progeny released near the upper end will be found near the lower end.

Accordingly, the upper end and the lower end are not neutronically connected together, and it is mathematically possible to physically define the entirety with one value of k. I can't say that. As the system approaches criticality, it tends to be joined together. Therefore, it can be said that Equation (1) locally defines k. In order to distinguish between the above-mentioned k and the effective multiplication factor of the entire system, the following description defines k as the reactivity.

In the comparative characteristic diagram of FIG. 4, a curve 16 (dotted line) indicates a spent fuel estimated from the height distribution of fissile nuclides remaining in the spent fuel assembly of the boiling water reactor. It shows a typical vertical reactivity distribution during storage of a fuel assembly in a conventional storage device, and a typical fuel assembly used in a boiling water reactor effectively utilizes nuclear fuel material. From the viewpoint of utilization, it is designed to burn as evenly as possible during the entire period of use as fuel for the nuclear reactor.

However, the neutron flux for maintaining the fission reaction is lower around the reactor core than in the reactor core, and there is a tendency for fissile nuclides to remain. For this reason, in the fuel assembly used in the nuclear reactor, the reactivity is higher at the upper end portion and the lower end portion of the fuel assembly always forming the peripheral portion of the core of the reactor than at the central portion of the fuel assembly. Becomes

FIG. 4 shows a typical reactivity distribution in the height direction of the spent fuel assembly of this boiling water reactor.
When the height position of the fuel effective portion 17 of the conventional arbitrary fuel body shown by the dotted line and the fuel effective portion 18 of the adjacent fuel body are stored at the same height position, the reaction to the axial position is As shown by the curve 16 (dotted line), a high-reactivity region is formed at about 3/24 of the active fuel length from the upper and lower ends of the active fuel area. 20 to 30% higher than the reactivity in the central region. The present invention has been made by paying attention to the characteristic of the reactivity distribution in the height direction of the spent fuel assembly.

The effective multiplication factor of a system in which the system shown in the plan view of FIG. 1 extends infinitely in the plane direction can be calculated by a diffusion theory well known in reactor physics. The characteristic diagram of FIG. 5 is based on the calculation based on the diffusion theory, and shows the spent fuel of a typical boiling water reactor having the reactivity distribution in the height direction shown by the curve 16 (dotted line) in the characteristic diagram of FIG. For the assembly, the effective multiplication factor of the infinite system in the plane direction changes with the difference between the fuel storage height positions of the fuel effective portions 17 and 18 due to the fuel bodies stored in the adjacent fuel storage pipes as a parameter. It shows how it goes.

In FIG. 5, the difference between the height of the fuel storage pipe H and the height of the fuel storage pipe 11 provided with the difference in the height of the fuel storage is 1/24 of the active fuel length ( 15 cm) is shown as one unit (hereinafter referred to as a node). According to FIG. 5, as the difference between the fuel storage height positions of the H pipe 11 and the L pipe 12, that is, the difference between the fuel effective section 17 and the fuel effective section 18 increases, the first three nodes (about Up to 45 cm), the effective gain gradually decreases, and thereafter, the effective gain gradually decreases.

The fuel effective portion 17, formed by the H pipe 11 and the L pipe 12,
In the range where the difference between the 18 fuel storage height positions is changed from 0 node to 24 nodes, the effective multiplication factor is up to about 10% Δk.
The difference between the fuel storage height positions of the H pipe 11 and the L pipe 12 can be reduced by three nodes (that is, 3/24 of the active fuel length).
Only the H pipe 11 and the L pipe 12 have different fuel storage height positions), it is possible to reduce the effective multiplication factor to about 5% Δk, which is half of that.

As described above, the H pipe 11 is used only for 3/24 of the active fuel length.
The effective gain can be effectively reduced by constructing a system in which the fuel storage height of the L pipe 12 differs from that of the boiling water reactor shown in the curve 19 (solid line) in FIG. It can be easily estimated from the reactivity distribution in the height direction of the storage system of the spent fuel assembly (the relative distribution shape is almost the same for one fuel assembly). In addition, since the distribution form is similar between one body and many bodies, it will be described with reference to FIG.

That is, in the reactivity distribution in the height direction of the spent fuel assembly of the conventional boiling water reactor shown by the curve 16 (dotted line) in FIG. In a state where there is no difference 20 in the fuel storage height position of the fuel effective portion 18 of the fuel body adjacent thereto, these regions having high reactivity are adjacent to each other, and the fuel is moved from the upper end and the lower end of the fuel effective portions 17 and 18. A region with high reactivity is formed at a portion of about 3/24 of the effective length.

In contrast, curve 19 of FIG.
In the (solid line), by setting the fuel storage height difference 20 between the H pipe 11 and the L pipe 12 to 3 nodes and arranging the fuel effective section 17 and the fuel effective section 18, the upper part in the height direction of the system H tube 11
The area of high reactivity at the top of the tube and the area of high reactivity at the bottom of the L-tube 12 at the lower part of the system in the height direction are adjacent to the non-reactive water area. The effective multiplication factor becomes smaller.

Incidentally, in the recent design of a boiling water reactor fuel assembly, in order to reduce the leakage of neutron flux from the upper and lower parts of the fuel assembly and utilize the nuclear fuel material more effectively, A device has been devised in which fuel pellets made of natural uranium, called blankets, are arranged above and below the effective portion.

In the fuel assembly designed as described above, the reactivity distribution in the height direction of the storage system of the spent fuel assembly of the boiling water reactor shown by the curve 19 (solid line) in FIG. The region of high reactivity moves to the center by the length of the blanket, but until the region of high reactivity is adjacent to the water region having no reactivity, the fuel in the H pipe 11 and the L pipe 12 A similar effect can be obtained by providing a difference in the storage height position.

That is, since the length of the blanket is usually one or two nodes, the three nodes without the blanket and four or five nodes obtained by adding the one or two nodes are used.
H only for nodes (ie, 4/24 to 5/24 of active fuel length)
By providing a difference 20 between the fuel storage height positions of the pipe 11 and the L pipe 12, the same effect as described above can be obtained. In addition,
As matters to be considered when putting the present invention into practical use, the operability of the fuel assembly 1 when the fuel assembly 1 is stored in or taken out of the fuel storage rack is cited.

That is, when the difference between the fuel storage height positions of the H pipe 11 and the L pipe 12 is too large, when the fuel assembly 1 is stored in or taken out of the fuel storage rack, the adjacent fuel assemblies 1 It may be a problem such as collision.
However, the difference 20 in the fuel storage height position shown in the present invention is 3/24 to 3/24 of the active fuel length of the fuel assembly including the locally high reactivity region in the fuel assembly height direction.
If it is about 5/24, there is no possibility that the operability will be affected when viewed from the full length.

If the upper ends of the H pipe 11 and the L pipe 12 are made to coincide with each other, the operability will not be impaired. However, if the difference 20 in the fuel storage height position is extremely large, the fuel storage facility will Disadvantages such as an increase in space loss in the fuel axial direction and a problem in radiation shielding properties occur. Furthermore, since the effects of the present invention can be realized by using a metal material that has been conventionally used, new performance verification of the material and the like is not required, and practical use can be achieved in a relatively short time.

FIG. 6 is a plan view showing a second embodiment of the present invention, in which a large number of H tubes 11 and L tubes 12 (a total of 90 tubes are 9 × 1).
0) The fuel storage rack 21 is arranged in a square shape, and its outer periphery is surrounded by the wall of the large container 13. In the square shape, the H pipe 11 and the L pipe 12 are alternately arranged in the vertical and horizontal directions in the figure. Has been placed. Also, in this fuel storage rack 21, the H pipe 11 and the L pipe 12 are spaced from each other by the wall of the large container 13, so that it is not always necessary to integrate the H pipe 11 and the L pipe 12 with each other. .

FIG. 7 is a plan view showing a third embodiment of the present invention, in which a large number of H tubes 11 and L tubes 12 are arranged in a square (a total of 90 tubes is 9 × 10), and the outer periphery thereof is formed. The fuel storage rack 22 is constituted by being surrounded by the wall of the large container 13. In the square arrangement, the same fuel storage height position is arranged in the vertical direction, while the H pipe 11 and the L The tubes 12 are arranged alternately in two rows. Note that the H tube 11 and the L tube 12 are spaced apart from each other by the wall of the large container 13 as in the second embodiment, so that it is not necessary to integrate the H tube 11 and the L tube 12 with each other. Not necessarily.

The effect of the invention when the system of the second and third embodiments shown in FIGS. 6 and 7 continues infinitely in the plane direction will be described. First, in the system in which the system of the second embodiment continues indefinitely, focusing on a certain diagonal direction in FIG. 6, the same fuel storage height position is arranged, and the fuel storage height is located on both sides thereof. Those at different positions are arranged. Therefore, it is possible to regard the system in which the first embodiment shown in FIG. 1 described above is infinite, although it is a rough approximation, that the pitch in the horizontal direction has increased by a factor of √2.

In FIG. 7, the system in which the system of the third embodiment continues infinitely can be regarded as a system in which the first embodiment continues infinitely, in which the lateral pitch is doubled. . The difference between the fuel storage height positions of the H pipe 11 and the L pipe 12 for a typical spent fuel assembly of a boiling water reactor having the reactivity distribution in the height direction shown in the characteristic diagram of FIG. Table 1 shows the difference in effective multiplication factor between the case where there is no (curve 16 (dotted line)) and the case where the difference is 3 nodes (curve 19 (solid line)) for the first to third embodiments. .

[0037]

[Table 1]

In this case, one pitch is equal to the minimum width of the fuel storage pipe that can store the fuel assembly of the boiling water reactor, and is about 15 cm. According to the results in Table 1, the effect of the present invention (difference in effective multiplication factor) tends to decrease as the pitch increases.

The operability of the fuel assembly 1 when the fuel assembly 1 is housed in the fuel storage rack 10 or taken out of the fuel storage rack 10 is more operable in the third embodiment than in the first embodiment. However, since the H tube 11 and the L tube 12 are arranged in two rows, it may be advantageous. Therefore, when the demand for the criticality safety of the fuel storage rack is not so large, the method of arranging the fuel storage tubes shown in the third embodiment may be selected according to the operability of the fuel assembly 1.

While the fuel storage rack 10 for storing the fuel assembly 1 of the boiling water reactor has been described above, the fuel storage rack 10 for storing the fuel bundle from which the channel box is removed from the fuel assembly 1 is also used. Of course, the present invention can be applied not only to racks but also to fuel transport / storage containers. Further, the present invention is also applicable to a fuel storage device that stores a fuel body for a pressurized water reactor.

Although the above description has exemplified a fuel assembly having a square cross section, the fuel storage device according to the present invention is applicable to a polygonal fuel assembly and a rectangular fuel assembly. Thus, the same operation and effect as those of the above embodiment can be obtained. Although the present invention has been described in the above embodiment in the case where spent fuel is stored in the vertical (height) direction in the axial direction, the same operation and effect can be naturally obtained by storing it in a horizontal state. It is clear.

[0042]

As described above, according to the present invention, the fuel storage device can be put to practical use in a relatively short period of time by using conventionally used materials, while maintaining a large number of fuel bodies in a sufficiently subcritical state. It can be stored more densely, has fewer installation locations, and has the effect of improving criticality safety.

[Brief description of the drawings]

FIG. 1 is a plan view of a fuel storage rack accommodating a fuel assembly according to a first embodiment of the present invention.

FIG. 2 is a bottom vertical sectional view taken along the line AA in FIG. 1;

FIG. 3 is a perspective view of an upper part of a fuel storage rack according to the first embodiment of the present invention.

FIG. 4 is a comparison characteristic diagram of a relationship between an axial position and a reactivity of a fuel body according to the present invention and the prior art.

5 is a characteristic diagram showing a relationship between an effective multiplication factor and an axial displacement in a system in which the system shown in FIG. 1 continues infinitely.

FIG. 6 is a plan view of a fuel storage rack according to a second embodiment of the present invention.

FIG. 7 is a plan view of a fuel storage rack according to a third embodiment of the present invention.

FIG. 8 is a top perspective view of the fuel assembly.

FIG. 9 is a plan view of a fuel storage rack containing a fuel assembly according to a conventional example.

FIG. 10 is a perspective view of an upper part of a conventional fuel storage rack.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fuel assembly, 2 ... Handle, 10, 21, 22 ... Fuel storage rack, 11 ... High fuel storage pipe (H
Pipe), 12 ... low fuel storage pipe (L
Tube), 13… Large container, 14… Storage height, 15… Pedestal, 16… Curve (dotted line), 17, 18… Fuel effective part, 19… Curve (solid line), 20
... the difference in fuel storage height position.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-128196 (JP, A) JP-A-59-10892 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G21C 19/07 G21C 19/40

Claims (1)

(57) [Claims] 1. A fuel storage device comprising a plurality of fuel storage tubes for storing fuel bodies, wherein one or more fuel storage tubes adjacent to each other in a fuel body storage axial direction position in an arbitrary fuel storage pipe. A fuel storage apparatus characterized in that the active fuel length of a fuel body including a region having a high degree of reactivity locally in the axial direction of the fuel storage body and in the axial direction of the fuel body is varied from 3/24 to 5/24.